Electronically scanned microwave antennas



1966 F. REGGIA ETAL 3,268,901

ELECTRONICALLY SCANNED MICROWAVE ANTENNAS Filed Feb. 25, 1963 2 Sheets-Sheet l flown/e0 5. James, Je.

Aug. 23, 1966 F. REGGIA ETAL 3,268,901

ELECTRONICALLY SCANNED MICROWAVE ANTENNAS Filed Feb. 25, 1963 k 2 Sheets-Sheet 2 Inyankom: Frank 'R 1':

--/MMIM/-% mu mm M j United States Patent by the Secretary of the Army Filed Feb. 25, 1963, Ser. No. 260,927 8 Claims. (Cl. 343-768) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment to me of any royalty thereon.

This invention relates to microwave antennas and more particularly to a microwave beam scanning antenna.

The antenna systems of the type herein contemplated comprise a number of radiator elements which are spaced along and coupled to a microwave transmission line, the transmission line being in the form of a rectangular waveguide. Microwave energy applied to the transmission line is coupled to the array of radiator elements and radiated therefrom in a directional pattern, the characteristic of the pattern being dependent upon the physical spacing and the relative electrical phasing of the radiator elements, and also upon the configuration of the array formed by these elements. A scanning action of this radiated pattern through a space angle is achieved by varying the electrical phasing of the radiating elements.

In general, the waveguide antenna must itself satisfy several major requirements to yield a practical radiating antenna array. To avoid objectionable side lobes and have the radiated energy concentrate predominantly along a main axis of di-rectiv-ity the radiator elements should have a spacing along the line of the array not greater than approximately three-fourths of a free-space wave length AM), and preferably the radiators should be spaced about one-half of a free-space wave length /2)\,,). With a suitable arrangement of the radiating elements the radiated energy will be focused into a beam, and the radiation pattern of the array may be rapidly moved-i.e., scanned-by varying the relative phase of the energy radiated by each of the elements. In general, the amount of scanning which may be obtained is proportional to the amount of phase shift which may be introduced between radiating elements.

It is an object of the present invention to provide a compact, efiicient, electronically scanable microwave antenna array.

Another object of this invention is the provision of a compact microwave antenna which can scan a focused radio beam over a large angle.

A further object of the present invention is to provide a compact beam scanning microwave antenna wherein the radiating elements may be spaced close enough to achieve a high degree of directivity and efiiciency while still permitting a large phase shift between radiators.

An additional object of this invention is to permit greater flexibility in a scanning microwave antenna by making the antenna array characteristics substantially independent of the phase shifter characteristics.

Still another object of this invention is to provide a compact beam scanning microwave antenna which uses ferrite phase shifters to alter the phase between radiating elements without causing amplitude modulation of the radiated beam.

Yet another object of the present invention is to provide a compact beam scanning microwave antenna using ferrite phase shifters in a highly efficient manner, whereby a large amount of phase shift may be introduced in a small space.

The foregoing objects, and other objects, features and advantages of the invention which will appear from the 7 Patented August 23, 1966 description and from the claims appended hereto, are attained by providing a plurality of radiators along a waveguide in the direction of propagation. The antenna is essentially a series-fed array of slot or dielectric rod radiators with means intermediate these radiating elements to cause a variable amount of relative phase shift between elements. The phase shift means include ferrite phase shifters in combination with means lying transverse to the broad dimension of the guide to concentrate the microwave energy in the phase shifters. The ferrite phase shifters are thereby placed outside the direct line of propagation along the radiating elements, with coupling to the waveguide in the H plane of the guide so that the optimum spacing between the radiators may be maintained, while still achieving large phase shifts.

The invention will be more fully understood by reference to the following detailed description accompanied by the drawings in which:

FIG. 1 is a partial sectional view of one form of the frequency scan antenna of this invention.

FIG. la is a sectional detail view of a E plane bend used in FIG. 1.

FIG. 2 is a plan view and partial section of the antenna of FIG. 1.

FIG. 3 is a perspective partial cut away view of another embodiment of a beam scanning microwave antenna in accordance with the teachings of this invention.

FIG. 4 is a detailed sectional view of the antenna of FIG. 3.

FIG. 5 is a plan view of the antenna section shown in FIG. 4.

FIG. 6 is a schematic sectional view of a two-way antenna.

FIGS. 1 and 2 show a microwave beam scanning antenna 10 which is comprised of a section 11 of conductively bounded electrical transmission line for guiding wave energy. More specifically 11 is a rectangular waveguide of the metallic shielded type having a wide internal cross-sectional dimensions b of at least one-half wavelength of the energy to be conducted therein and a narrow dimension a substantially one-half of the wide dimension. The waveguide 11 is dimensioned to propagate energy in the dominant or TE mode with the electric vector extending parallel to the narrow wall. While not limited thereto, the antenna contemplated is well suited for operation in the X band region. The left hand end of the antenna 10 is connected to a source of microwave energy which is to be radiated, and the right hand end 12 of the antenna is terminated to prevent reflection, as is common in the art. Distributed along the longitudinal axis of the antenna are a plurality of radiators 13, which are shown as a series of transverse slots in the broad face of the rectangular waveguide 10, but may also be dielectric radiators if desired. Spaced between each of the radiating elements 13 are a plurality of ferrite phase shifters indicated generally at 14.

The ferrite phase shifters 14 are located on one of the broad walls of the waveguide 11. The longitudinal axis of the antenna 10 and the longitudinal axis of the phase shifters 14 are essentially perpendicular to allow close slot spacing. The outer wall 19 of the phase shifters 14 is conductively joined to the broad wall of the waveguide 11, forming E plane corners at 28 and 29.

Each of the phase shifters 14 is comprised essentially of two transmission type ferrite phase shifters 16 and 17 of the type described in the article, A New Technique in Ferrite Phase Shifting for Beam Scanning Microwave Antennas by F. Reggia and E. G. Spencer published in Proceedings IRE, vol. 45, No. 11, November 1957. The two ferrite rod phase shifters 16 and 17 are used back to back to produce twice the phase shift possible with one alone while not increasing the length of the phase shifter 14. The ferrite rod phase shifter 16 includes a ferrite rod 18 located within a non-symmetrical rectangular waveguide section (its narrow, E plane dimension at cutoff) formed by an outer wall 19, which is merely a continuation of the lower broad wall of the guide 10, and an inner wall 21 which is common to both halves of the phase shifter. The right hand phase shifter 17 is identical to the left hand phase shifter 16 just described. As is taught in the aforesaid article, to produce a phase shift in the microwave energy propagated through the ferrite rod, a longitudinal magnetic field is applied to the ferrite rod 18 by coil 22, and the diameter of the ferrite rod 18 is increased to a point where a large percentage of the microwave energy is concentrated in the rod, while the rectangular waveguide boundary formed by the walls 19 and 21 is sufficiently below cutoff to suppress rotation due to the Faraday effect of the ferrite. Phase shifts in excess of 300 degrees per .inch with relatively small applied magnetic fields have been obtained with MgMn ferrites at X-band frequencies with only small changes in transmitted power. Reversing the direction of the field applied by the coils 22 or the direction of propagation gives the same phase delay, and in this manner the antenna may be used as a two way antennai.e., transmitreceive. 1

The separate halves of the phase shifters 14 are joined together by 180 E plane waveguide bends 23 which have a zero radius of curvature in order to conserve space between radiators along the length of the array. As is shown in the detail of FIG. la, the center of curvature for the bend 23 is the end of the common wall 21 and the radius of curvature R is equal to the distance between the waveguide walls 19 and 21. This zero radius bend is made by choosing an impedance matching pin 24 and adjusting it along the center line of the common guide wall to obtain the best impedance match looking in either direction. At X band frequencies, the diameter of the pin 24 is bi -inch and its center should be located about the same distance from the common wall 21.

Located transverse to the electric vector of the dominant mode propagated in the waveguide are a series of 90 E plane miterbends 25 and 26. As shown in FIG. 1 with the direction of energy propagation from left to right, the 90 E plane bend 25 diverts the energy into the phase shifter 14, and the 90" E plane bend 26 diverts the energy leaving the phase shifter back to the waveguide 10.

i In operation, microwave energy generated by the transmitter 11 is propagated along a short section of the rectangular waveguide 10 with the E plane of the dominant mode perpendicular to the direction of propagation. The energy is diverted by the 90 E plane miterbend 25 into the first of the phase shifters 14. It propagates down the left hand side 16 of the phase shifter 14, is guided by the 180 E plane bend 23 into the right hand side 17, and is diverted by the 90 E plane miter 26 back to the waveguide 10 where a portion of the energy is radiated from the .slot 13. The process is continued throughout the length of the antenna 10 with a portion of the energy being radiated from each of the slots 13. The radiated beam is caused to scan by applying a phase modulating voltage to each of the coils 22 of the phase shifters 14, whereby the relative phase of the energy radiated from each of the slots is varied.

Referring now to FIG. 3, there is shown an alternate embodiment for obtaining the large phase shifts required while maintaining close spacing of the radiating elements of a beam scanning antenna. The antenna is comprised of a section of rectangular waveguide 31 similar to the waveguide 10 of FIG. 1. The waveguide 31 is adapted to receive microwave energy at the left-hand end,32, and is terminated in a non-reflective impedance at its other end. The waveguide 31 has a plurality of radiating elements 34 and between adjacent radiating elements there are phase modulators 35. In accordance with this aspect of the present invention a series of E plane T sections are used in combination with a nonreciprocal circulator. The phase modulators 35 are mounted on one broad wall of the waveguide 31 with an outer wall 47 connected to the lower wall of the waveguide 31 forming two E plane corners 45 and 46 so that the phase modulator 35 forms one arm of a T section, and sections of the waveguide 31 on either side of the phase modulator 35 form the other two arms. The circulator is an E plane T-type circulator, and includes a rod or post 36 of gyromagnetic material, such as ferrite, mounted at the junction of the three arms of the T with its longitudinal axis parallel to the plane of the H vector of the dominant microwave mode transmitted in the section. A unidirectional magnetic field oriented substantially parallel to the longitudinal axis of the rod 36 is applied by any suitable means, such as permanent magnet 37.

The intensity of the magnetic field in not critical but should be greaterthan saturation magnetization and less than that which produces ferromagnetic resonance in the ferrite. Due to the non-reciprocal action of the longitudinally magnetized ferrite rod placed at the junction of the phase modulator 35, the energy being propagated along the waveguide 31 is directed into the phase modulator 35.

The phase modulator 35 is a reflection type phase shifter, and is similar in operation to the phase shifter 14 of FIG. 1. A detailed explanation of the specific reflection type phase shifter can be found in A Reciprocal Phase Modulator for Rapid-Scanning Microwave Antennas, by Frank Reggia, published in the Proceedings of the 1959 Army Science Conference, United States Military Academy, West Point, N.Y., June 2426, 1959, vol. 2. The phase shifter consists of a ferrite rod 38 located in a short section of waveguide 39 having its narrow dimension (E plane dimension) slightly below cutofi. The end of the short section of guide 39 is terminated in a short-circuit impedance 41, which may be adjustable to tune the initial position of the antenna beam as shown in FIG. 4. A variable longitudinal magnetic field is produced in ferrite rods 38 by means of coils 42.

In operation, energy propagated in the rectangular waveguide 31 is directed by the circulator rod 36 into the phase shifter 35. The energy in the phase shifter 35 is concentrated in the ferrite rod 38 and is phase modulated in accordance with a modulating voltage applied to the winding 42. In this manner the relative phase between adjacent radiators 34 is caused to vary -to produce the scanning action of the antenna. The microwave energy, reflected by the termination 41, undergoes an additional phase shift as it travels back along the 'rod 38. The circulator rod 36 then directs the energy toward the next radiating element 34 as is shown by the arrows. With the use of the reflection type phase shifter, twice the phase shift per unit length is obtained over what could be obtained :with a transmission type phase shifter, and additionally, a space saving is achieved by the elimination of one matching taper.

The amount of circulation obtained with the rod circulator 36 depends upon the diameter of the ferrite rod 36, its position relative to the phase shifter 35, and the strength of the applied magnetic field. i

Applicant has achieved good ciroulationapproximate- 1y 0.1 db insertion loss and approximately 25 db isolation-in an X band antenna of the following dimensions: Standard waveguide (rectangular) rg52/ u for Xband:

Dimension a 0.400 inch.

Dimension b 0.900 inch.

Dimension c 0.125 inch. Rod 36:

Material MgMn ferrite.

Diameter 0.100 inch. Frequency range 9300 mc.9400 mc. Magnetic field intensity 2000 oer.

Several modifications will be apparent to those skilled in the art. For example it is not necessary that the radiating elements be located in the broad face of the guide; they may in some cases be located in the narrow face of the guide if desired, as is well 'kHOlWn in the art. Additionally, the nonreciprocal one way antenna of FIGS. 3, 4 and 5 may be modified into a two way antenna replacing the three port cir-culator with a four port circulator as shown in FIG. 6.

In FIG. 6 energy propagated from left to right along a waveguide 51 is directed by a ferrite rod circulator 52 into a reflection type rphase modulator 53, where the phase of the energy is varied by means of a modulating signal applied to a winding 54. After the energy leaves the phase shifter 53 a portion of it is radiated from a radiator 55 which is a diagonal slot in the narrow side of the waveguide 51. On transmission from right to left the energy, detected by the slots 55 for example, is directed by the circulator rod 52 into a reflection type phase shifter 56 where it is phase modulated by the winding 57. In this way, a two way (transmit-receive) antenna can be constructed.

The embodiments shown are only exemplary and var ious modifications can be made in construction and arrangement within the scope of the invention as defined in the appended claims.

We claim as our invention:

1. A compact, efiicient beam scanning microwave antenna comprising, in combination, 1

(a) A hollow rectangular iwaveguide section for propagating transverse electric waves, said waveguide section having a -pair of broad walls and a pair of narrow walls with the electric vector of an applied transverse electric wave extending substantially parallel to said narrow walls,

(b) A plurality of radiating elements in said rectangular waveguide and spaced along a longitudinal axis of the antenna so that radiated energy will form a directive beam,

(c) Ferrite phase shifters located between said radiating elements, said ferrite phase shifters including a longitudinally magnetized ferrite rod centrally disposed in an asymmetrical waveguide section, so that energy propagated in said phase shifter is substantially concentrated in said ferrite rod,

((1) Said ferrite phase shifters mounted on one of said broad walls with the longitudinal axis of said antenna and the longitudinal axis of said asymmetrical waveguide section being essentially perpendicular, said rectangular waveguide sections and said asymmetrical waveguide sections being conductively joined together forming -E plane corners with means in said rectangular waveguide to direct the microwave energy into and out of said phase shifters whereby energy may be substantially fully coupled from one of said waveguide sections to the other waveguide section and thereby allow a large phase shift of the propagated energy between radiating elements in a short distance along the longitudinal axis of the antenna,

(e) And means to vary the longitudinal magnetization applied to said ferrite rods whereby the relative phase between radiating elements may be varied causing the radiated beam to scan.

2. A compact, efficient, beam scanning microwave antenna system comprising in combination;

of the antenna so that radiated energy will form a directive beam,

(c) Ferrite phase shifters located between said radiating elements, each of said ferrite phase shifters including a pair of longitudinally magnetized ferrite rods and a pair of asymmetrical waveguide sections, one of said ferrite rods being centrally located in one of said asymmetrical waveguide sections, and the other of said rods centrally in the other of said asymmetrical waveguide sections so that energy propagated in said asymmetrical wave-guide sections will be substantially concentrated in said ferrite rods, said pair of asymmetrical waveguide sections being connected together at one end by a zero radius 180 degree E plane bend,

(d) Said ferrite phase shifters being mounted on one of said broad walls with the longitudinal axis of said antenna and the longitudinal axis of each'of said pair of asymmetrical waveguide sections being essentially perpendicular, said rectangular wave-guide section and each of said pair of asymmetrical waveguide sections being conductively joined together forming E plane corners,

(e) Each phase shifter having a first degree E plane bend directing energy propagated along the longitudinal axis of said antenna into the first of said pair of asymmetrical waveguides, and a second 90 degree E plane bend directing microwave energy propagated in the second of said pair of asymmetrical waveguides back along the longitudinal axis of said antenna, whereby energy is substantially fully coupled from one of said rectangular waveguide sections to the asymmetrical waveguide sections, thereby allowing a large phase shift of the propagated energy bctween radiating elements in a short distance along the longitudinal axis of the antenna,

(f) And means to vary the longitudinal magnetization applied to said ferrite rods whereby the relative phase between radiating elements may be varied causing the radiated beam to scan.

3. Acompact eificient, beam scanning microwave antenna system comprising in combination,

(a) A hollow rectanguler waveguide section for propagating transverse electric waves, said waveguide section having a pair of broad walls and a pair of narrow walls, the electric vector of an applied transverse electric wave extending substantially parallel to the narrow walls,

(b) A plurality of radiating elements in the rectangular waveguide and spaced along a longitudinal axis of the antenna, so that radiated energy will form a directive beam.

(0) Ferrite phase shifters located between said radiating elements, said ferrite phase shifters including a longitudinally magnetized ferrite rod and an asymmetrical waveguide section short circuited at one end, said ferrite rod being centrally disposed in said asymmetrical waveguide section so that energy propagated in said asymmetrical Waveguide is concentrated predominantly in said ferrite rod,

((1) Said ferrite phase shifters mounted on one of said broad walls with the longitudinal axis of said antenna and the longitudinal axis of said asymmetrical waveguide section being perpendicular, said rectangular wave guide sections and said asymmetrical waveguide sections being conductively joined together l t l l applied to said ferrite phase shifter rods whereby the relative phase between radiating elements may be varied causing a radiated beam to scan.

4. A compact, efficient, beam scanning microwave antenna as in claim 3 wherein said E plane circulator includes a longitudinally magnetized ferrite circulator rod located at the E plane T junction, said circulator rod extending transverse to the longitudinal axis of the antenna and perpendicular to the electric vector propagated in both the rectangular waveguide and in the asymmetrical waveguide.

5. A compact, efiicient, beam scanning microwave antenna as in claim 1 wherein said radiating elements are slots in the other broad face of the rectangular waveguide, said slots being transverse to the longitudinal axis of the antenna.

6. A compact, efiicient, beam scanning microwave antenna as in claim 3 wherein said radiating elements are slots in the other broad face of the rectangular waveguide, said slots being transverse to the longitudinal axis of the antenna.

7. A compact, efficient, beam scanning microwave antenna as in claim 3 wherein means are provided to adjust the location of the short circuit in the asymmetrical waveguide whereby the antenna may be tuned.

8. A compact, efiicient beam scanning two way microwave antenna comprising in combination;

(a) A hollow rectangular waveguide section for propagttin-g transverse electric waves, said waveguide section having a pair of broad walls and a pair of narrow walls, the electric vector of an applied transverse electric wave extending substantially parallel to the narrow walls,

(b) A plurality of radiating elements in a narrow wall of the rectangular waveguide spaced along a longitudinal axis of the antenna so that radiated energy will form a directive beam.

(c) Two ferrite phase shifters located between said radiating elements, each of said ferrite phase shifters including a longitudinally magnetized ferrite rod and an asymmetrical waveguide section short cirouited at one end, said ferrite rods being centrally disposed in said asymmetrical waveguide sections so that energy propagated in said asymmetrical waveguide is concentrated predominately in said ferrite rod,

(d) One of said pairs of phase shifters being located on one broad face of said rectangular waveguide, and the other of said phase shifters being located on the other broad face of said rectangular waveguide, the longitudinal axis of said antenna and the longitudinal axes of said asymmetrical waveguide sections being perpendicular, said rectangular waveguide sections and said asymmetrical waveguide sections being conductively joined together forming a pair of E plane Ts.

(e) An E plane circulator means disposed in said rectangular waveguide to direct the energy propagated along the longitudinal axis of the antenna into one of said pair of phase shifters or the other of said .pairs of phase shifters depending upon the direction of propagation of energy in said rectangular waveguide, and also to direct energy leaving said phase shifters backalong the longitudinal axis of the antenna.

(f) And means to vary the longitudinal magnetiza tion applied to said ferrite rods whereby the relative phase between radiating elements may be varied causing the radiated beam to scan.

No references cited.

HERMAN KARL SAALBACH, Primary Examiner. E. LIEBERMAN, Assistant Examiner. 

1. A COMPACT, EFFICIENT BEAM SCANNING MICROWAVE ANTENNA COMPRISING, IN A COMBINATION, (A) A HOLLOW RECTANGULAR WAVEGUIDE SECTION FOR PROPAGATING TRANSVERSE ELECTRIC WAVES, SAID WAVEGUIDE SECTION HAVING A PAIR OF BROAD WALLS AND A PAIR OF NARROW WALLS WITH THE ELECTRIC VECTOR OF AN APPLIED TRANSVERSE ELECTRIC WAVE EXTENDING SUBSTANTIALLY PARALLEL TO SAID NARROW WALLS, (B) A PLURALITY OF RADIATING ELEMENTS IN SAID RECTANGULAR WAVEGUIE AND SPACED ALONG A LONGITUDINAL AXIS OF THE ANTENNA SO THAT RADIATED ENERGY WILL FORM A DIRECTIVE BEAM, (C) FERRITE PHASE SHIFTERS LOCATED BETWEEN SAID RADIATING ELEMENTS, SAID FERRITE PHASE SHIFTERS INCLUDING A LONGITUDINALLY MAGNETIZED FERRITE ROD CENTRALLY DISPOSED IN AN ASYMMETRIAL WAVEGUIDE SECION, SO THAT ENERGY PROPAGATED IN SAID PHASE SHIFTER IS SUBSTANTIALLY CONCENTRATED IN SAID FERRITE ROD, (D) SAID FERRITE PHASE SHIFTERS MOUNTED ON ONE OF SAID BOARD WALLS WITH THE LONGITUDINAL AXIS OF SAID ANTENNA AND THE LONGITUDINAL AXIS OF SIAD ASYMMETRICAL WAVEGUIDE SECTION BEING ESSENTIALLY PERPENDICULAR, SAID RECTANGULAR WAGEGUIDE SECTIONS ANS SAID ASYMMETRICAL WAVEGUIDE SECTIONS BEING CONDUCTIVELY JOINED TOGETHER FORMING E PLANE CORNERS WITH MEANS IN SAID RECTANGULAR WAVEGUIDE TO DIRECT THE MICROWAVE ENERGY INTO AND OUT OF SAID PHASE SHIFTERS WHEREBY ENERGY MAY BE SUBSTANTIALLY FULLY COUPLED FROM ONE OF SAID WAVEGUIDE SECTIONS TO THE OTHER WAVEGUIDE SECTION AND THEREBY ALLOW A LARGE PHASE SHIFT OF THE PROPAGATED ENERGY BETWEEN RADIATING ELEMENTS IN A SHORT DISTANCE ALONG THE LONGITUDINAL AXIS OF THE ANTENNA, (E) AND MEANS TO VARY THE LONGITUDINAL MAGNETIZATION APPLIED TO SAID FERRITE RODS WHEREBY THE RELATIVE PHASE BETWEEN RADIATING ELEMENTS MAY BE VARIED CAUSING THE RADIATED BEAM TO SCAN. 